The present invention is directed toward a method and apparatus for coupling a semiconductor die to die terminals.
Semiconductor dies are typically encased in a plastic shell or package prior to installation in microelectronic devices. The plastic package makes the die easier to handle during installation and protects the die from dust, dirt and other contaminants after it has been installed. The package includes package terminals, such as pins or other similar devices which have one end coupled to the bond pads of the die and an opposite end accessible outside the package. The ends of the package terminals accessible outside the package may be coupled to other microelectronic components, linking the die to those components.
FIG. 1 is a top isometric view of a representative conventional die package 10. FIG. 2 is a partially broken top plan view of the conventional die package 10 shown in FIG. 1. Referring to FIGS. 1 and 2, the die package 10 comprises a plastic body 12 housing a die 20 therein. For purposes of clarity, the top portion of the body 12 is shown in phantom lines in FIG. 1 and partially broken away in FIG. 2. The die 20 includes bond pads 21 that are coupled to circuitry within the die. The bond pads 21 are also coupled with wire bonds 50 to leadfingers 40 that extend outwardly away from the die to the edges of the die package 10 where they are coupled to pins 30. The pins 30 project outwardly beyond the edges of the body 12 and may be coupled with other electronic components in a conventional manner so that the die 20 may communicate with the other components.
One problem with the conventional die package 10 described above is that the leadfingers 40 may limit the minimum size of the die package and die 20. The ends of the leadfingers 40 must have a surface area which is large enough to permit the bond wires 50 to be easily coupled thereto. The leadfingers 40 must also be large enough to secure the die 20 in a selected position as the die is encapsulated in the body 12 during manufacture of the die package 10. The large surface area of the leadfingers 40 and the spacing between adjacent leadfingers may limit the minimum size of the die package 10. The size and spacing of the leadfingers 40 may also limit the minimum distance between the corresponding bond pads 21 to which the leadfingers are connected and may accordingly limit the minimum size of the die 20.
Another problem with the conventional die package 10 described above is that the leadfingers 40 may increase the capacitance measured at the pins 30, thereby reducing the speed with which signals may propagate between the pins 30 and the corresponding bond pads 21. The reduced signal speed may decrease the overall speed and efficiency of the die 20 and the microelectronic components with which the die is coupled.
Yet another problem with the conventional die package 10 shown in FIGS. 1 and 2 is that an impedance measured at one of the pins 30 may be different than an impedance measured at another pin 30. The impedance mismatch between pins 30 of the same die 20 probably adversely affects the relative timing of signals coupled to the die through different pins 30.
In another conventional arrangement (not shown), the die 20 may be coupled to leadfingers 40 which are positioned directly on the surface of a printed circuit board. The printed circuit board may then be coupled to other microelectronic devices or other printed circuit boards. This alternate arrangement may suffer from the same problems discussed above, including a limited minimum die size, reduced signal speed and mismatched impedances.
The present invention is directed toward a method and apparatus for coupling a semiconductor die to terminals of a die package or printed circuit board which supports the die. An apparatus in accordance with one embodiment of the invention includes a microelectronic device comprising a semiconductor die having at least one terminal. The microelectronic device further comprises a conductive member elongated between a first end portion and a second end portion. The second end portion is proximate to the terminal of the die. The conductive member has an intermediate portion between the first and second end portions that is narrower than the second end portion. In one embodiment, the second end portion is positioned adjacent the semiconductor die, and in another embodiment, the second end portion is positioned on a surface of the semiconductor die. In either embodiment, the second end portion may be coupled to the die terminal with a conductive coupler.
In another embodiment of the invention, the microelectronic device comprises a package having first and second package terminals and a semiconductor die positioned within the package and having first and second die terminals. A first conductive member is coupled at one end to the first package terminal. A first conductive coupler is coupled between the first die terminal and the first conductive member. The microelectronic device further comprises a second conductive member coupled at one end to the second package terminal.
A second conductive coupler is coupled between the second die terminal and the second conductive member. The first conductive member and first conductive coupler are selected to produce a first impedance at the first package terminal and the second conductive member and second conductive coupler are selected to produce a second impedance at the second package terminal. The first and second impedances are selected to be approximately equal.
In still another embodiment, the semiconductor die may be positioned on the surface of a printed circuit board or other substrate. The substrate may include conductive members that are offset relative to each other and the semiconductor die. The conductive members may be coupled to the die terminals with conductive couplers and may also be connected to vias in the substrate.
The present invention is also embodied in a method for positioning conductive members proximate to first and second adjacent terminals of a semiconductor die. In one embodiment, the method comprises positioning an end of a first conductive member proximate the first terminal of the die and positioning an end of a second conductive member proximate the second terminal of the die. The ends of the first and second conductive members are staggered such that the end of the second conductive member is spaced apart from the second terminal by a distance which is greater than the distance between the end of the first conductive member and the first terminal.
The present invention is also embodied in a method for selecting the impedance of a conductive path between a terminal of a semiconductor die and a terminal of a package in which the die is housed. In one embodiment, the method comprises selecting a size and material of a conductive member to have a first impedance and selecting a size and material of a conductive coupler to have a second impedance. The conductive member has first and second opposite ends and the method further comprises connecting the first end of the conductive member to the terminal of the package and connecting the conductive coupler to extend between the terminal of the die and the second end of the conductive member.